The increasing automation of most manufacturing processes has spawned a great variety of robotic devices for handling materials and parts during such procedures. These range from heavy duty industrial devices to smaller precision devices, and they may be designed to accomplish a single specific purpose or to be of a more general utility. A subclass of such devices are robotic arms which are designed to position an object at any point within a fixed cylindrical space. An example of this latter sort of device is taught by U.S. Pat. No. 4,813,845 issued to Swain, which teaches a unique means for moving objects within a planar circular zone and provides for the addition of a conventional elevator mechanism as a means to extend the movement along the vertical longitudinal axis of a cylindrical zone.
In the semiconductor manufacturing industry, materials handling robots may be used for a number of purposes. Primary among these is the handling of silicon wafers. Of course, this procedure is done in a clean room environment and it requires that the robot be capable of a great deal of precision of movement. The most common type of apparatus currently in use for this purpose is a general purpose robot having a vertical cylinder with means for rotating the cylinder (around a "8" axis) and means for elevating the cylinder (along a vertical or "Z" axis), as desired. Additionally, a means is provided for extending and retracting an arm with an object carrying hand at its end within a planar circular zone (as for example, along an "R" axis, which is here defined as being a path described by a radius of the planar circular zone within which the object carrying hand may be moved), which zone is perpendicular to the vertical axis of the cylinder and has its center located at the junction of the top of the cylinder and the cylinder's vertical center axis. While such robotic devices are provided by various manufacturers and thus vary in many respects, all of the prior art devices here being discussed share the characteristics heretofore described. Indeed, it is considered to be necessary that such devices adhere to this general configuration, as the market demands that such devices be "interchangeable" in the sense that a new entry into the market place should be capable of movement within a zone similar to that attainable by existing machines.
However, such devices as have existed in the prior art embody several undesirable qualities. One of these is that the means for powering the arm and hand reside within the cylinder. This means that the mass of the cylinder is considerable, which adds to the rotating mass of the cylinder and places a great deal of that mass toward the top of the cylinder. The increased mass is undesirable because it increases inertia of the cylinder and thus reduces the responsiveness thereof to control signals, which may be manifested by an increase in what is known in the art as "following error". The fact that the center of mass of the cylinder is shifted toward the top is undesirable because it increases the need for support at the top of the cylinder to prevent wobble in the cylinder top. Indeed, all of the prior art devices within the inventor's knowledge have required cam follower type devices located around the perimeter of the cylinder to support the cylinder. These cam follower devices are themselves a source of potential problems, as they tend to become less precise with wear and can contribute contaminants to the environment as a result of such wear or because of lubricants used in conjunction therewith. Furthermore, the cam followers and their housings add considerable mass to the apparatus, which detracts from its responsiveness. Also, placement of a motor within the cylinder contributes to unwanted contaminants, as motors are themselves sources of contaminating particles. Prior to the present invention, it has been considered to be necessary to use supporting means at or near the top of a housing for supporting the Z axis traversing mechanism.
All of the prior art cylindrical area robotic devices within the inventor's knowledge have had arm powering means located within the cylinder and/or have required supporting means near the top of the cylinder housing.
No prior art cylindrical area robotic device configuration to the inventor's knowledge has successfully removed the means for producing or transferring power for Z axis motion from within that portion of the device which carries the arm along the Y axis. All successful applications to date have further required a supporting means located at or near the top of the Z axis cylinder housing (or equivalent mechanism).